Investigation Of Contaminated Sites Research Articles

Theoretical assessment of influential factors and application in chlorinated hydrocarbon detection with membrane interface probe

The membrane interface probe (MIP) is an efficient and economical in-situ tool for chlorinated hydrocarbon (CH) contaminated site investigation. Given that the interpretation of MIP test is currently limited to a qualitative level, a theoretical model considering multiphase flow and multifield coupling is firstly proposed to simulate MIP test process. This model can consider phase change, membrane effect, adsorption and dissolution of the CH liquid, gas diffusion, and evaporation. Then, the model is used to study the changes in soil temperature and soil CH concentration during MIP test, as well as the influences of soil CH concentration and soil properties (initial water saturation, soil intrinsic permeability, and thermal properties) on MIP response. Finally, a simplified MIP interpretation model is developed based on parametric analysis results and verified against field and laboratory test data. It is found that the soil CH concentration, rather than soil properties, dominates the MIP response. The simplified interpretation model can deliver practical prediction of the CH concentration through the detected results by MIP, which may improve the applicability of MIP.

Interpretable machine learning for predicting the fate and transport of pentachlorophenol in groundwater

Pentachlorophenol (PCP) is a commonly found recalcitrant and toxic groundwater contaminant that resists degradation, bioaccumulates, and has a potential for long-range environmental transport. Taking proper actions to deal with the pollutant accounting for the life cycle consequences requires a better understanding of its behavior in the subsurface. We recognize the huge potential for enhancing decision-making at contaminated groundwater sites with the arrival of machine learning (ML) techniques in environmental applications. We used ML to enhance the understanding of the dynamics of PCP transport properties in the subsurface, and to determine key hydrochemical and hydrogeological drivers affecting its transport and fate. We demonstrate how this complementary knowledge, provided by data-driven methods, may enable a more targeted planning of monitoring and remediation at two highly contaminated Swedish groundwater sites, where the method was validated. We evaluated 6 interpretable ML methods, 3 linear regressors and 3 non-linear (i.e., tree-based) regressors, to predict PCP concentration in the groundwater. The modeling results indicate that simple linear ML models were found to be useful in the prediction of observations for datasets without any missing values, while tree-based regressors were more suitable for datasets containing missing values. Considering that missing values are common in datasets collected during contaminated site investigations, this could be of significant importance for contaminated site planners and managers, ultimately reducing site investigation and monitoring costs. Furthermore, we interpreted the proposed models using the SHAP (SHapley Additive exPlanations) approach to decipher the importance of different drivers in the prediction and simulation of critical hydrogeochemical variables. Among these, sum of chlorophenols is of highest significance in the analyses. Setting that aside from the model, tetra chlorophenols, dissolved organic carbon, and conductivity found to be of highest importance. Accordingly, ML methods could potentially be used to improve the understanding of groundwater contamination transport dynamics, filling gaps in knowledge that remain when using more sophisticated deterministic modeling approaches.

High‐Resolution Geological Information from Crosshole Ground Penetrating Radar in Clayey Tills

AbstractHeterogeneous glacial deposits dominate large parts of the Northern Hemisphere. In these landscapes, high‐resolution characterization of the geology is crucial for understanding contaminant transport. Geological information is mostly obtained from multiple boreholes drilled during a site investigation, but such point‐based data alone do not always provide the required resolution to map small‐scale heterogeneity between boreholes. Crosshole ground penetrating radar (GPR) is suggested as a tool for adding credible geological information between boreholes at contaminated site investigations in industrial sites where infrastructure, such as electrical installations, can pose a challenge to other geophysical methods. GPR data are sensitive to the dielectric permittivity and the bulk electrical conductivity, which can be related to the distribution of water content and sand/clay occurrences. Here we present a detailed crosshole GPR dataset collected at an industrial contaminated site in a clay till setting. The data are processed using a novel inversion approach where information on changes in the velocity and attenuation of the radar signal are obtained independently. The GPR results are compared to borehole logs, grain size analyses, and relative permeability data from the site. The GPR data analysis provided valuable information on the understanding of the lateral geological variability. A silt layer with a thickness of a few decimeters, likely important for flow characterization, was confirmed and resolved by GPR data. Our findings suggest that crosshole GPR has the potential for contributing with high‐resolution geological information by filling the data gap between boreholes, thereby becoming a relevant tool in contaminated site investigations.

Characterization and sampling of a deep and heterogeneous aquifer – An application to the Paleocene – Eocene aquifer in the Aquitaine basin, France

Groundwater sampling in boreholes has been carried out for decades according to well-established protocols and regulations. An important requirement in this context is the need to purge the borehole prior to any sampling action, the volume of the purge being adapted to the water flow and the regulatory context. Contaminated site investigations have introduced the concept of water column heterogeneity in the screened section of boreholes, which also occurs in some uncontaminated boreholes or in long-screened boreholes. Specific guidelines and practices were thus introduced, in particular the concept of discrete sampling. This type of sampling can be advantageously used in deep boreholes, provided that there is some renewal of water at the screens or the perforated intervals. The present study aims to take a step forward in the characterization of deep boreholes set up in the Aquitaine basin in France, by defining a protocol for relatively short boreholes (depth < 170 m) and applying it to much deeper boreholes, formerly drilled for oil and gas exploration (sampling up to 1035 m deep). Acquisitions were performed to better characterize water chemistry, including some isotope considerations. They were based on physico-chemical logging and endoscopic inspections where technically possible. After a review of the information provided by the investigations on the characterization of the Paleocene – Eocene aquifer in southwestern France, a methodology is proposed to make sampling in deep boreholes with low-yield more reliable, by combining the abstraction of a reduced water volume and the use of a downhole sampling system.

Noninvasive survey technology for LNAPL-contaminated site investigation

Nonaqueous-phase liquids (NAPLs) usually move through the vadose zone not in a homogeneous spread manner but in the form of disconnected blobs, and they remain in the pores of porous media. A major challenge in remediating an NAPL-contaminated site is to detect and delineate the distribution of NAPLs. Geophysical technologies could act as investigating methods for sites with limited resources and time constraints. Based on the principle of magnetometric resistivity (MMR) method, in this study, we applied an electric current flow pattern and its resulting magnetic field to develop a new application for contaminated site investigation. The physical phenomena about the magnetic distribution, the flow pattern of electric current, and the influence of different media in packed sand were observed via sandbox experiments. A field test was performed at a light NAPL (LNAPL)-contaminated site by combining the magnetic field survey and a soil sample analysis. Two potential contaminated zones were determined according to the specific characteristics of the contour image plotted according to the magnetic field intensity collected on the ground. The quantitative results of the total petroleum hydrocarbons (TPHs) of 18 soil samples were used to verify the results of the magnetic field survey. The comparison results revealed that we obtained a high accuracy of 92.9% in the field test, which indicated that this technology could be used to investigate LNAPL-contaminated sites. Moreover, two phenomena, the scale effect led to poor resolution and the behavior of flow pattern disturbance distorted the survey images, were observed in both the sandbox experiment and the field test.

Rationale for Soil‐Gas Sampling to Improve Vapor Intrusion Risk Assessment in China

Rationale for Soil‐Gas Sampling to Improve Vapor Intrusion Risk Assessment in China

Reflection waveform inversion of ground-penetrating radar data for characterizing thin and ultrathin layers of nonaqueous phase liquid contaminants in stratified media

Accurately quantifying thin-layer parameters by applying a targeted reflection waveform inversion methodology to ground-penetrating radar (GPR) reflection data may provide a useful tool for near-surface investigation and especially for contaminated site investigation where nonaqueous phase liquid (NAPL) contaminants are present. We implemented a targeted reflection waveform inversion algorithm to quantify thin-layer permittivity, thickness, and conductivity for NAPL thin ([Formula: see text] dominant wavelength [Formula: see text]) and ultrathin ([Formula: see text]) layers using GPR reflection data. The inversion used a nonlinear grid search with a Monte Carlo scheme to initialize starting values to find the global minimum. By taking a targeted approach using a time window around the peak amplitude of the reflection event of interest, our algorithm reduced the complexity in the inverse problem. We tested the inversion on three different synthetic data sets and four field data sets. In all testing, the inversion solved for NAPL-layer properties within 15% of the measured values. This algorithm provides a tool for site managers to prioritize remediation efforts based on quantitative assessments of contaminant quantity and location using GPR.

Potential of Photoionization Detector for Organic Compounds Analysis at a Brownfield Site Investigation

Photoionization detector (PID) provided an efficient and inexpensive approach for many gas and vapor analytes. Using PID as a real-time diagnostic tool in contaminated site investigation has been addressed in this study in comparison with post-time GC-MS detection. Total pollutant concentrations from selected field soil samples were calculated by addition of each VOCs and SVOCs contaminant concentration detected via an Agilent 6890 GC-MS, while portable photoionization detector (PPID) values were recorded in real-time during site investigation. Contamination distributions were plotted based on PPID readings and GC-MS data respectively. The results showed a positive correlation between PPID readings and contaminants concentrations, suggesting that PPID reading could be used as a qualitative tool to characterize the approximate range of pollutants. The accuracy of PPID reading for VOCs and SVOCs detection at contaminated site investigation could be optimized by calibration and specialized measurement protocols.

The use of spatial autocorrelation analysis to identify PAHs pollution hotspots at an industrially contaminated site

The identification of contamination "hotspots" are an important indicator of the degree of contamination in localized areas, which can contribute towards the re-sampling and remedial strategies used in the seriously contaminated areas. Accordingly, 114 surface samples, collected from an industrially contaminated site in northern China, were assessed for 16 polycyclic aromatic hydrocarbons (PAHs) and were analyzed using multivariate statistical and spatial autocorrelation techniques. The results showed that the PCA leads to a reduction in the initial dimension of the dataset to two components, dominated by Chr, Bbf&Bkf, Inp, Daa, Bgp, and Nap were good representations of the 16 original PAHs; Global Moran's I statistics indicated that the significant autocorrelations were detected and the autocorrelation distances of six indicator PAHs were 750, 850, 1,200, 850, 750, and 1,200 m, respectively; there were visible high-high values (hotspots) clustered in the mid-bottom part of the site through the Local Moran's I index analysis. Hotspot identification and spatial distribution results can play a key role in contaminated site investigation and management.

Paleo-Roothole Facilitated Transport of Aromatic Hydrocarbons through a Holocene Clay Bed

A field study involving high-resolution core sampling of a 0.5-2 m thick clay bed was undertaken at a contaminated former industrial facility in the UK to establish the nature and significance of preferential contaminant flowpaths. In contrast to most previous research, the focus was upon a buried aquitard, in this case a Holocene lagoonal clay located 6 m below ground surface and overlain by a sand aquifer impacted by historic nonaqueous phase liquid hydrocarbon spills. The study, involving 11 cores over a 630 by 150 m area, demonstrated that the presence of paleo- (i.e., preupper sand) rootholes controlled the degree of dissolved-phase benzene penetration into the aquitard. Where homogeneous, largely paleoroot-free clay is present (hydraulic conductivity 3 x 10(-5) m/d.), contaminant concentrations in the clay decline rapidly with depth: modeling showed the dominant transport process to be diffusion. In other cores, elevated benzene concentrations deep in the clay require advection to have occurred, presumably along preferential pathways. The latter were shown by thin sectioning, core slice mapping and 3-D X-ray tomography to be organic matter lined rootholes of < 2 mm aperture. The significance of such preferential pathways was confirmed quantitatively by measuring hydraulic conductivity (0.04 m/d) and calculating flux, the latter being over 10 times greater than expected from steady state diffusion. Our study hence demonstrates paleoenvironmental control of modern-day contaminant transport through a clay aquitard. It is suggested that many subaerial unconformities in mudrocks, especially those associated with even rudimentary paleosol development would lead to permeability enhancement and therefore afford substantially reduced protection against migrating contaminants. In contaminated site investigations, it is hence necessary to consider the aquitard paleoenvironment and not just the main rock type present.

Glacio-lacustrine stratigraphy, aquifer characterization and contaminant transport: a case study in South Lake Tahoe, California, USA

A hydrogeologic model that has been used by many researchers and consultants to describe an area of South Lake Tahoe, California, USA impacted by MTBE contamination describes a relatively homogeneous unconfined aquifer comprised of poorly sorted glacial outwash deposits, within which water-supply wells are able to exert significant alteration in natural groundwater flow. A re-examination of the area’s hydrogeology is presented, which supports a layered heterogeneous aquifer system constructed of alternating fine and coarser-grained glacio-lacustrine depositional units. This re-evaluation was accomplished through a review of lithologic logs across an area of approximately 1 km2, combined with observations of significant hydraulic head differences and knowledge of the depositional environments controlled by Pleistocene Lake Tahoe high stands. Many of the fine-grained units observed at depths from 6 to 15 m, although relatively thin, are generally continuous and serve as significant barriers to groundwater flow. The vertical migration of contamination across these fine-grained units to deeper groundwaters was facilitated by cross-screened monitoring wells installed as part of site investigation activities. This conclusion highlights the importance of geologic characterization and proper monitoring well construction at contaminated site investigations.

Contaminated site investigation and remediation of chlorinated aromatic compounds

The high degree of public concern and anxiety about chlorinated aromatic compounds persisting in the environment mandate that effective clean-up methods be found to eliminate their hazard. The factors that lead to the implementation of such techniques are found to vary significantly according to economic factors, site locations, and community perceptions. The disposal of chlorinated aromatic compounds has become a major environmental and social problem. Due to their chemical stability and resistance to degradation, their presence in the environment poses a potential health hazard to humans and other organisms. This investigation reviews the methods currently in use for the remediation of chlorinated aromatic compounds in soils and sediments and examines the factors that lead to the implementation of each technique under specific conditions. An experimental program has also been conducted to investigate the effectiveness of low temperature dechlorination of PCB contaminated soil. From the bench-scale experiments performed, it could be determined that the potential exists for scale-up to accommodate larger quantities of soils and sediments. Destruction and removal efficiency (DRE) exceeding 99% show that by manipulation of controlled conditions, further improvements in the degradation of polychlorinated biphenyls (PCBs) from soils can be attained. Preliminary studies using a novel process have shown that low temperatures and controlled conditions can achieve reduction of PCBs in soils and sediments from 1000 to below 10 ppm. The augmentation of an alkaline source and saturated steam diffusing across the fixed bed was found to contribute substantially to the dechlorination process. In experiments conducted to date, altering conditions in a tube furnace have determined how dechlorination can best be promoted. This has entailed optimising reaction times, temperatures and the augmentation of additives.

Effect of humic substances on Cu(II) solubility in kaolin-sand soil

The type and amount of organic matter present in industrially contaminated soils will influence the risk they pose. Previous studies have shown the importance of humic and fulvic acids (FAs) (important components of soil organic matter) in increasing the solubility of toxic metals but were not carried out using toxic metal levels and the pH range typical of industrially contaminated soils. This study investigated the influence of three humic substances (HSs: humates, fulvates and humins) on the solubility of copper(II) ions in kaolinitic soil spiked with Cu at levels representative of industrially contaminated soil. Humates, fulvates and humin were extracted from Irish moss peat, and controlled pH batch leaching tests were conducted on an artificial kaolin-sand soil that was spiked with each. Further leaching tests were conducted on soil spiked with each HS and copper nitrate. Dissolved organic contents were determined by titration and total and free aqueous copper concentrations in the leachate were measured using AAS and ion selective electrode (ISE) potentiometry respectively (dissolved complexed copper levels were determined by difference). It was found that humates and fulvates are partially sorbed by the soil, probably by chemisorption on positively charged gibbsite (Al-hydroxide) sites in the kaolinite. The addition of 340 mg/kg Cu(II) ions did not significantly affect the amount of humate or fulvate sorbed. Dissolved humates and fulvates form soluble complexes with copper over the pH range 3–11. However, in the presence of kaolinite, soluble copper humates and fulvates are unable to compete with the kaolinite for Cu ions at pH 6–7. Above pH 8, humate and fulvate complexes are the only forms of dissolved Cu. Humin is largely insoluble and has little effect on Cu mobility between pH 2 and 12. The implication of this study is that measurement of total soil organic content and water leaching tests should be a standard part of contaminated site investigation.

Managing Petroleum Contaminated Soil: Department of Transportation Perspective

Federal and state policies governing contaminated site investigations and remediation strategies have evolved over the past several years. Advances in treatment technologies, especially in situ methods of remediation, are largely responsible for this evolution. However, public opinion has also influenced environmental regulators and helped to shape policy. In dealing with issues of contamination, especially in conjunction with on-going construction projects, making appropriate choices on how to handle petroleum-contaminated soil requires more than comparing costs of treatment methods and weighing the advantages and disadvantages of various cleanup options. Selection of a remediation technique to clean up a site must take into account the community in which the site is located. Local governmental agencies and public opinion can play a strong role in determining what remediation actions are allowable, especially regarding highly visible ex situ treatments. The ability to choose among methods of soil treatme...

A contaminated site investigation: comparison of information gained from geophysical measurements and hydrogeological modeling

The investigation of contaminated sites is usually a long and expensive process. It is therefore desirable to use a combination of methodologies in an integrative approach that can reduce redundant information gathering. The objective of this study was to examine the usefulness of 2 non-intrusive exploration techniques in a contaminated site investigation. Borehole positioning based on geophysical measurements was compared to positioning based on the Bayesian expert system for flow-field modeling. The goal set at the field site was the assessment of the type and load of contaminants transported from the landfill site to the adjacent aquifer and the extent of leachate plumes within the groundwater. The two methods made different demands on information gathering and were found to be complementary. The geophysical approach focused attention on the waste compartments at the site and on mixing plumes in the adjacent aquifer but could not, without prior information, provided information on the flow field. The Bayesian approach to flow-field modeling determined areas of greatest model uncertainty at the model boundaries. The model highlighted areas of greatest uncertainty that might otherwise have been overlooked and provided information on the most likely mean direction of the leachate plumes. It was concluded that both methods contribute to a site investigation and should be used before additional drilling is carried out.

Modification of Heterotrophic Plate Counts for Assessing the Bioremediation Potential of Petroleum-Contaminated Soils

Bioremediation is becoming an accepted treatment option for the remediation of petroleum-contaminated sites. Instrumental in implementing bioremediation is the characterization of bacteria capable of degrading the contaminants of interest. A wide variety of techniques have been reported in the literature but they often involve volatile solvents or petroleum mixtures as substrates and thus are difficult to use. Standard heterotrophic plate counts are often required by environmental regulations to be included as part of contaminated site investigations and assessments. Standard heterotrophic plate count techniques were found in this study to be unable to detect changes in population sizes in contaminated and uncontaminated soils. A more specific assay using benzoate, a metabolite of many BTEX compounds, was also used. This technique was capable of detecting differences in population size between contaminated and uncontaminated soils and benzoate is thus a better substrate to use when characterizing petroleum-contaminated soils. Furthermore, the data (population size vs. contaminant concentration) fit a hyperbolic model well. Such a model could be used to monitor population size with respect to contaminant concentration as well as population size outside the contaminant plume to further assess the progress of bioremediation at a contaminated site.

Dielectric Sensors Used in Environmental and Construction Engineering

ABSTRACTDielectric properties of materials can give insight into the microstructure or concentrations of their constituents and can be determined by measuring the complex impedance of a capacitor formed by a set of electrodes with the material as the dielectric. Measuring frequencies between 1 MHz and 1 GHz appeared to be most informative for soil and concrete. A new dielectric sensor containing an integrated circuit that includes all analog and digital circuitry is described briefly. This sensor is used to demonstrate the potential of dielectric sensor technology for applied materials research in the field in two recently developed applications. One application concerns the determination of the state of hardening of young concrete. The relationship shown is between changes in the dielectric properties and changes in the structure for curing concrete. The other application is a dielectric probe for contaminated site investigation. It appeared to be possible to locate chemically polluted soil layers, such as with chlorinated solvents or oil, using small changes in their dielectric properties.

The use of expert systems for determining sampling strategies in contaminated site investigations

Sampling in site investigations is mostly done on the basis of hit or miss probing. Several mathematical and (geo)statistical methods are available for improving the reliability of sampling procedures. Combining these tools with the knowledge of experts in a so-called soft-knowledge based computer program is an excellent way of rationalizing sampling strategies.